In recent years, lighting optical systems are being developed that contain a fluorescent material that emits fluorescent light when irradiated by excitation light. This type of lighting optical system is used in, for example, projection-type display apparatuses.
The lighting optical system disclosed in International Publication No. 2012/127554 (hereinbelow referred to as Patent Document 1) includes a laser light source and a phosphor unit. A phosphor region and a reflection region are formed on one surface of the phosphor unit. The phosphor region has a phosphor that emits fluorescent light of a predetermined wavelength when irradiated by laser light. The reflection region is a region that reflects light. The phosphor unit is configured to freely rotate around an axis of rotation that is orthogonal to the surface on which the reflection region and phosphor region are provided. Laser light is incident to the phosphor unit during the rotation of the phosphor unit, whereby the fluorescent light from the phosphor and laser light that is reflected by the reflection region area are emitted sequentially.
The illuminance of light emitted from the lighting optical system is dependent on the quantity of light that is emitted from the phosphor. One of the characteristics of phosphor is that heat generation reduces light-emitting efficiency. Accordingly, it is preferably to reduce phosphor heat generation in order to reduce any decrease in illuminance of light that is emitted from the lighting optical system.
Phosphor heat generation results from the irradiation of laser light. In the lighting optical system described in Patent Document 1, the phosphor is cooled by air flow received by the phosphor unit itself with the rotation of the phosphor unit. However, it is preferable that the cooling effect of cooling the phosphor is improved.